1. Field of the Invention
The invention relates to the field of programmable logic controllers which are used to control machinery and equipment for automated and partially automated assembly lines. The controllers are programmed by the use of ladder diagrams wherein elements of a ladder diagram represent relays, switches and the like associated with the equipment and machinery on the assembly line.
2. Prior Art
Prior art programmable logic controllers can be directly coupled to up to 16 peripheral controllers which serve to interface the assembly line machinery and equipment to the programmable logic controller. Additionally, prior art programmable logic controllers can indirectly control six additional racks of sixteen peripheral controllers by using local rack adapters, there being one local rack adapter for each rack of sixteen peripheral controllers, for a total of 896 inputs and 896 outputs (assuming 8 inputs and 8 outputs per peripheral controller). Ladder diagrams which are, in effect, the program used by the programmable logic controller to generate the appropriate control, data and address signals for the peripheral controllers, are created and edited using a separate processor such as a personal computer or minicomputer. The completed ladder diagram is recorded on magnetic tape or disk which is removed from the processor which created the ladder diagram, and read into the memory of the programmable logic controller through a disk or tape drive connected to the programmable logic controller. A representative prior art programmable logic controller is a Model 700 Controller manufactured by Square D Company.
Prior art ladder editors are typically part of the programming panel of the prior art programmable controllers.